Acrylonitrile-butadiene-styrene graft copolymer resins (hereinafter, ABS resins) generally can have good impact resistance, processability, mechanical strength, heat distortion temperature and colorability. Therefore, ABS resins have been widely used in the production of electric or electronic goods, automobile parts, office automation (OA) instruments, and the like.
However, ABS resins can have poor weatherability, because of the many chemically unstable double bonds in the butadiene rubber component. Accordingly, ABS resins can readily deteriorate upon exposure to ultraviolet rays. For this reason, weather stabilizers are commonly added to ABS resins during extrusion processes. Even with the addition of weather stabilizers, however, the resulting molded article may still not exhibit sufficient weatherability because of the butadiene rubber component.
In an attempt to address this problem, a chemically stable acryl rubber or a rubbery polymer of butadiene and acrylic monomer can be used instead of the butadiene rubber.
Acrylate-styrene-acrylonitrile graft copolymers (hereinafter, ASA resin) prepared by graft copolymerizing acrylic rubber, styrene and acrylonitrile monomer have been widely used in the production of various products such as automobiles, agricultural devices, and electric or electronic goods, which are used outdoors and which require weatherability.
Because the ASA resin does not have chemically unstable double bonds, it may have good weatherability. However, the ASA resin can exhibit inferior impact resistance.
To address this concern, methods for imparting impact resistance to ASA resin have been proposed, which can employ rubber components having large-sized particles or which can lower the gel content of the rubbery polymer. However, these methods can have drawbacks, such as difficulty in controlling the physical properties of a graft copolymer and poor surface gloss. Further, methods using acrylic rubber lattices having different particle sizes could not overcome the above problems.
As noted herein, ASA resins are terpolymers of acrylate-styrene-acrylonitrile and can have good weatherability, as well as chemical resistance and heat stability. Accordingly, as also noted here in, ASA resins have been used in various outdoor applications which take advantage of the weatherability of such resins. Examples of such products can include outdoor electric or electronic parts, automobile parts, building materials, agricultural implements, ASA/ABS sheets, profile extrusions, sign posts, outdoor products, sports products, interior articles, leisure products, home appliances, sports products, and the like, and further including satellite antenna, kayak paddles, sash joiners, door panels and side-view mirror housings. However, the relatively poor colorability and insufficient impact resistance at room temperature and at low temperature make these ASA resins less favored for more demanding applications. Accordingly, there remains a need for improved weatherable ASA resins which maintain desirable properties regardless of temperature and have good colorability.
U.S. Pat. No. 3,426,101, Japanese Patent Publication Laid-Open Nos. 4-180949, 5-202264 and 7-316243 and German Patent Publication No. 1260135 are directed to methods for preparing weatherable ASA resins. These patents employ butadiene rubber as a core and a rubber copolymer comprising alkylacrylate rubber as a shell. However, these methods are considered disadvantageous, because the polymerization is complicated and it can be difficult to control the reaction. Further, the butadiene rubber in the core may cause a decrease in weatherability under bad weather conditions. Moreover the ASA resins show poor colorability.
Korean Patent No. 10-0440474 is directed to an ASA-based thermoplastic resin composition having good low temperature impact resistance. The ASA-based thermoplastic resin composition comprises two kinds of alkylacrylate rubber latex cores having different sizes and a SAN copolymer grafted into the rubber latex. However, the resulting molded article does not exhibit sufficient colorability and the method for preparing the above ASA-based thermoplastic resin can be expensive because the method separately prepares two acrylate latex cores.
Korean Patent No. 10-0477944 is directed to an ASA graft copolymer composition which comprises a rubbery polymer consisting of an inner layer comprising 1,3-butadiene and an outer layer composed of alkyl acrylate monomer and aromatic vinyl compound; an alkyl methacrylate or alkyl acrylate compound; an aromatic vinyl compound; and a vinyl cyanide compound. However, the resulting molded article still exhibits poor colorability.
Further, U.S. Pat. No. 6,187,862 is directed to a grafted rubber comprising a substrate, a first grafted phase and a subsequent grafted phase which are sequentially grafted to the substrate, wherein the substrate contains a core containing the polymerization product of at least one vinylaromatic monomer, and a shell containing a crosslinked elastomer selected from the group consisting of polyalkyl acrylate, hydrogenated polydiene and polydiene. Although the resin composition using the grafted rubber features improved impact strength and weatherability, the low temperature impact strength and colorability are still insufficient.
Accordingly, there still exits a need for an improved ASA graft copolymer exhibiting desirable colorability, weatherability and impact resistance even at low temperatures.